A blood test to determine how fast someone is ageing has been shown to work on wild birds, offering support to claims that the technique could accurately predict a human's lifespan.

The research represents the first time the ageing test has been used successfully on animals living outside a laboratory setting. The test measures the average length of tiny structures on the tips of chromosomes, called telomeres, which are known to get shorter each time a cell divides during an organism's lifetime.

Telomeres are believed to act like internal clocks by providing a more accurate estimate of a person's true biological age rather than their actual chronological age. This has led some experts to suggest that telomere tests could be used to estimate how long they have left to live, assuming they die of natural causes.

At least one company is offering a £400 blood test in the UK (NZ$780) for people interested in seeing how fast they are ageing based on their average telomere length.

Telomere tests have been widely used on animals in experiments, now scientists have performed them on an isolated population of songbirds in the Seychelles.

"We saw that telomere length is a better indicator of life expectancy than chronological age. So by measuring telomere length we have a way of estimating the biological age of an individual - how much of its life it has used up," said David Richardson, of the University of East Anglia.

The researchers tested the average telomere lengths of a population of 320 Seychelles warblers on Cousin Island, which ornithologists have studied for 20 years.

"Our results provide the first clear and unambiguous evidence of a relationship between telomere length and mortality in the wild, and substantiate the prediction that telomere length and shortening rate can act as an indicator of biological age further to chronological age," says the study, published in the journal Molecular Ecology.

Studying an island population of wild birds was important because there were no natural predators and little migration.

"We wanted to understand what happens over an entire lifetime, so the Seychelles warbler is an ideal research subject," Dr Richardson said.

"We investigated whether, at any given age, their telomere lengths could predict imminent death. We found that short and rapidly shortening telomeres were a good indication that the bird would die within a year. We also found that individuals with longer telomeres had longer lifespans overall.

"It used to be thought that telomere shortening occurred at a constant rate in individuals, and that telomere length could act as an internal clock to measure the chronological age of organisms in the wild.

"However while telomeres do shorten with chronological age, the rate at which this happens differs between individuals of the same age. This is because individuals experience different amounts of biological stress due to the challenges and exertions they face in life. Telomere length can be used as a measure of the amount of damage an individual has accumulated over its life."